devel/py-fabric: Update to 2.5.0

Fabric 2 is not at 100% feature parity with 1.x! Some features have been
explicitly dropped, but others simply have not been ported over yet,
either due to time constraints or because said features need to be
re-examined in a modern context.

More information at:
https://www.fabfile.org/upgrading.html#upgrading
https://www.fabfile.org/upgrading.html#upgrade-specifics

Changelog: https://www.fabfile.org/changelog.html

Reviewed by: koobs (maintainer)
Approved by: koobs (maintainer)
Differential Revision: https://reviews.freebsd.org/D20683